Optical recording medium and production method therefor

ABSTRACT

An optical recording medium capable of suppressing warps arising during a long time use and a method of producing the same, which has the configuration of comprising a substrate  13,  an optical recording layer  14  formed on the substrate  13  and a light transmitting protective film  17  formed on the optical recording layer  14,  wherein the protective film  17  includes a polymer film  16  having a thermal shrinkage coefficient of 0.02% or less and an adhesive layer  15  for adhering the polymer film  16  to the optical recording layer  14.  As the polymer film  16,  those produced by a melt cast method, subjected to annealing processing in advance or having a residual solvent of 0.3% by weight or less in the film may be preferably used.

TECHNICAL FIELD

[0001] The present invention relates to an optical recording mediumhaving an optical recording layer for optically recording informationand a method of producing the same.

BACKGROUND ART

[0002] In recent years, studies on optical information recording methodshave been carried out in various places in a field of informationrecording. The optical information recording methods have a number ofadvantages such that noncontact recording and reproducing can beperformed and adopting to memory forms of read-only type,write-once-read-many type and rewritable type is possible, and a wideuse thereof from industrial use to consumer use has been considered asmethods of realizing an inexpensive large capacity file.

[0003] Achieving of a large capacity of optical recording media(hereinafter, also referred to as optical disks) for the above varietyof optical information recording methods has been made mainly byshortening the wavelength of the laser light used as a light source inan optical information recording method and by increasing the numericalaperture (NA) of the objective lens to make a spot size small on a focalplane.

[0004] For example, in CDs (compact disks), a laser light wavelength is780 nm, a numerical aperture (NA) of an objective lens is 0.45 and acapacity is 650 MB, while in DVD-ROMs (digital versatile disk-read onlymemory), the laser light wavelength is 650 nm, the NA is 0.6 and thecapacity is 4.7 GB.

[0005] Furthermore, in an optical disk system of the next generation, alarge capacity of 22 GB or more can be attained by making the laserlight wavelength 450 nm or less and the NA 0.78 or more by using anoptical disk wherein a thin light transmitting protective film (a coverlayer) of, for example, 100 μm or so is formed on an optical recordinglayer.

[0006]FIG. 1A is a schematic perspective view of an optical disk for theabove optical disk system of the next generation.

[0007] An optical disk D has an approximately disk shape with a centerhole CH formed at its center portion and is driven to rotate in thedrive direction DR.

[0008] When recording or reproducing information, a laser light of ablue to bluish violet color region or other light LT is irradiated on anoptical recording layer in the optical disk DC by an objective lens OLhaving a numerical aperture of, for example, 0.8 or more for being used.

[0009]FIG. 1B is a schematic cross-sectional view of the optical diskshown in FIG. 1A, and FIG. 1C is an enlarged cross-sectional view of akey portion of the schematic cross-sectional view of FIG. 1B.

[0010] One surface of a disk substrate 13 made by a polycarbonate resin,etc. having a thickness of 1.1 mm or so is provided with grooves 13 afor separating track regions and formed with an optical recording layer14 comprising for example a reflection film, a dielectric film, arecording film, another dielectric film, etc. stacked in this order. Theconfiguration and the number of layers of the optical recording layer 14differ in accordance with the type of recording material and design.

[0011] The above recording film is, for example, a recording film of aphase-change type, a magneto-optical recording film or a recording filmincluding an organic dye.

[0012] Furthermore, a light transmitting protective film 37 having afilm thickness of 0.1 mm composed of an adhesive layer 35 made by anadhesive or a pressure-sensitive tackiness agent film, etc. and apolymer film 36 is formed on the optical recording layer 14.

[0013] When recording or reproducing information on or from the aboveoptical disk, a light LT, such as a laser light, is irradiated on theoptical recording layer 14 by the objective lens OL from the protectivefilm 37 side.

[0014] When reproducing information from the optical disk, a returnedlight reflected on the optical recording layer 14 is received by a lightreceiving element, a predetermined signal is generated by a signalprocessing circuit and a reproduction signal is taken out.

[0015] In the optical disk as above, the optical recording layer 14 hasirregularity shapes in accordance with the grooves 13 a provided on onesurface of the disk substrate 13, and the track regions are separated bythe grooves 13 a.

[0016] For example, the regions which are projecting to the protectivefilm 37 side when viewing from the disk substrate 13 side are referredas “lands” L, while recessed regions are referred as “grooves” G.

[0017] For example, a land/groove recording method for recordinginformation both on the land and the groove can be adopted, and alsoonly one of the land and groove may be used as a recording area.

[0018] The above optical disk is an optical disk of a type ofirradiating a laser light to the optical recording layer 14 through theprotective film 37 and reading a reflected light, and thereby, it candeal with an increased numerical aperture.

[0019] A method of producing the above optical disk shown in FIG. 1A toFIG. 1C will be explained.

[0020] First, a disk substrate 13 made by a polycarbonate resin, etc.having a film thickness of 1.1 mm or so being formed on its surface anirregularity pattern for an optical recording layer is formed, forexample, by injection molding, on which an optical recording layer 14having a stacked layer body of a reflection film, a dielectric film, arecording film, another dielectric film is formed on the irregularitypattern in this film forming order, for example, by a spattering method,so that the optical recording layer 14 having a pattern corresponding tothe above irregularity pattern is formed.

[0021] Next, a polymer film 36 is adhered on the optical recording layer14 by an adhesive 35, such as an ultraviolet curing resin adhesive or apressure-sensitive tackiness agent film, so as to obtain a protectivefilm 37 composed of the adhesive layer 35 and the polymer film 36.

[0022] From the above, an optical disk having the configuration shown inFIG. 1 can be obtained.

[0023] In the optical disk of the above configuration, however, sincethe polymer film shrunk during a long time use, there was a problem thatwarps arose on the optical disk.

[0024] An amount of a coma aberration generated when the disk warp above(tangential or radial skew) arises is proportional to NA³/λ, so whenshortening wavelength of the laser light and increasing numericalaperture for a larger capacity, properties required to the optical diskbecome strict to suppress the coma aberration and the disk warp has tobe suppressed.

[0025] The disk warp above is described to be in the radial directionand in the tangential direction, but due to shrinkage of the polymerfilm, a warp mainly in the radial direction is largely changed.

DISCLOSURE OF INVENTION

[0026] The present invention was made in consideration of the abovecircumstances and has as an object thereof to provide an opticalrecording medium capable of suppressing a warp arisen during a long timeuse and a method of producing the same.

[0027] To attain the above object, an optical recording medium of thepresent invention comprises a substrate, an optical recording mediumformed on the substrate, and a light transmitting protective film formedon the optical recording layer; wherein the protective film comprises apolymer film having a thermal shrinkage coefficient of 0.02% or less andan adhesive layer for adhering the polymer film to the optical recordinglayer.

[0028] Preferably, in the above optical recording medium of the presentinvention, the polymer film is a polymer film produced by a melt castmethod.

[0029] Preferably, in the above optical recording medium of the presentinvention, the polymer film is a polymer film subjected to annealingprocessing after being produced as a film and before being adhered tothe optical recording layer in advance.

[0030] Preferably, in the above optical recording medium of the presentinvention, a residual solvent in the polymer film is 0.3% by weight orless.

[0031] The above optical recording medium of the present inventionincludes a polymer film having a thermal shrinkage coefficient of 0.02%or less and an adhesive layer for adhering the polymer film to theoptical recording layer as a light transmitting protective film on theoptical recording layer.

[0032] Here, the thermal shrinkage coefficient is a ratio of thermalshrinkage before and after annealing processing under a predeterminedcondition, such as annealing processing at 90° C. in the air for twohours, etc.

[0033] Shrinkage of the polymer film due to a temperature and humiditydoes not cause warps on an optical disk even after a long time under acertain condition of temperature and humidity, on the other hand,shrinkage due to evaporation of a residual solvent remained in thepolymer film and a relaxation of internal strain arises irreversibly,consequently, warps arise on the optical disk even under the abovepredetermined condition.

[0034] In the optical recording medium of the present invention, thethermal shrinkage coefficient of the polymer film is made to be 0.02% orless, and thereby, shrinkage of the polymer film is suppressed during along time use and arising of warps on the optical recording medium canbe suppressed.

[0035] As to the above polymer film, even when the thermal shrinkagecoefficient is more than 0.02%, it can be made in a range of 0.02% orless by performing annealing processing in advance before adhering tothe optical recording layer, so that the above effects can be obtained.

[0036] The annealing processing may be performed, for example, at 90° C.in the air for two hours by using a circulating drying furnace, a hotplate or an infrared heating furnace, and conditions of the annealingprocessing may be adjusted in accordance with a thermal shrinkagecoefficient of the polymer film.

[0037] Also, to attain the above object, a method of producing anoptical recording medium of the present invention includes the steps offorming an optical recording layer on a substrate, and forming a lighttransmitting protective film on the optical recording layer, wherein thestep of forming the protective film includes a step of adhering apolymer film having a thermal shrinkage coefficient of 0.02% or less tothe optical recording layer via an adhesive layer.

[0038] Preferably, in the above method of producing an optical recordingmedium of the present invention, a polymer film produced by a melt castmethod is used as the polymer film.

[0039] Preferably, in the above method of producing an optical recordingmedium of the present invention, annealing processing is performed onthe polymer film after the step of producing the polymer film as a filmand before the step of adhering to the optical recording layer inadvance.

[0040] Preferably, in the above method of producing an optical recordingmedium of the present invention, a polymer film wherein a residualsolvent in the polymer film is 0.3% by weight or less is used as thepolymer film.

[0041] In the above method of producing an optical recording medium ofthe present invention, an optical recording layer is formed on asubstrate, then, a light transmitting protective film is formed on theoptical recording layer. Here, the step of forming the protective filmincludes a step of adhering the polymer film having a thermal shrinkagecoefficient of 0.02% or less to the above optical recording layer by anadhesive layer.

[0042] According to the above method of producing an optical recordingmedia of the present invention, it is possible to produce an opticalrecording medium wherein a polymer film having a thermal shrinkagecoefficient of 0.02% or less is adhered to an optical recording layer byan adhesive layer as a light transmitting protective film, shrinkage ofthe polymer film is suppressed in a long time use and arising of warpsis suppressed.

BRIEF DESCRIPTION OF DRAWINGS

[0043]FIG. 1A is a perspective view of an optical disk according to aconventional example, FIG. 1B is a cross-sectional view and FIG. 1C isan enlarged cross-sectional view.

[0044]FIG. 2A is a perspective view of an optical disk according to afirst and second embodiments of the present invention, FIG. 2B is across-sectional view and FIG. 2C is an enlarged cross-sectional view.

[0045]FIG. 3A and FIG. 3B are cross-sectional views of a productionprocess of a method of producing the optical disk according to the firstembodiment of the present invention.

[0046]FIG. 4A is a cross-sectional view showing a process continued fromFIG. 3B and FIG. 4B is a cross-sectional view of a process continuedfrom FIG. 4A.

[0047]FIG. 5A is a schematic view of an injection molding processshowing a process continued from FIG. 4B and FIG. 5B is across-sectional view thereof.

[0048]FIG. 6A is a cross-sectional view showing a process continued fromFIG. 5A and FIG. 5B, and FIG. 6B is a cross-sectional view showing aprocess continued from FIG. 6A.

[0049]FIG. 7 is a schematic view for explaining a method of producing apolymer film by a melt cast method.

[0050]FIG. 8 is a perspective view for explaining a stamping process ofthe polymer film.

[0051]FIG. 9A is a perspective view showing a process continued fromFIG. 6B, and FIG. 9B is a perspective view showing a process continuedfrom FIG. 9A.

[0052]FIG. 10A is a perspective view showing a process continued fromFIG. 9B, and FIG. 10B is a perspective view showing a process continuedfrom FIG. 10A.

[0053]FIG. 11A and FIG. 11B are perspective views showing a productionprocess of a method of producing an optical disk according to a secondembodiment of the present invention.

[0054]FIG. 12A is a perspective view showing a process continued fromFIG. 11B, and FIG. 12B is a perspective view showing a process continuedfrom FIG. 12A.

[0055]FIG. 13A is a perspective view showing a process continued fromFIG. 12B, and FIG. 13B is a perspective view showing a process continuedfrom FIG. 13A.

[0056]FIG. 14A is a perspective view showing a process continued fromFIG. 13B, and FIG. 14B is a perspective view showing a process continuedfrom FIG. 14A.

BEST MODE FOR CARRYING OUT THE INVENTION

[0057] Below, the best mode for carrying out the invention will beexplained in detail with reference to the drawings.

[0058] First Embodiment

[0059]FIG. 2A is a perspective view of an optical recording medium(hereinafter, also referred to as an optical disk) according to thepresent embodiment.

[0060] An optical disk DC has an approximately disk shape with a centerhole CH formed at its center portion and is driven to rotate in thedrive direction DR.

[0061] When recording or reproducing information, a laser light of ablue to bluish violet color region or other light LT is irradiated on anoptical recording layer in the optical disk DC by an objective lens OLhaving a numerical aperture of, for example, 0.8 or more for being used.

[0062]FIG. 2B is a cross-sectional view of the optical disk shown inFIG. 2A, and FIG. 2C is an enlarged cross-sectional view of a key partof the cross-sectional view of FIG. 2B.

[0063] One surface of the disk substrate 13 made by, for example, apolycarbonate resin having a film thickness of 0.3 mm or more, forexample, 1.1 mm or so is provided with grooves 13 a for separating trackregions, such as “lands” L and “grooves” G, and an optical recordinglayer 14 is formed as an upper layer thereof.

[0064] The optical recording layer 14 has a configuration wherein, forexample, a reflection film, a dielectric film, a recording film andanother dielectric film, etc. are stacked in this order. The layerconfiguration and the number of layers of the optical recording layer 14differ in accordance with the type of recording material and design.

[0065] The above recording film is, for example, a recording film of aphase-change type, a magneto-optical recording film or a recording filmincluding an organic dye.

[0066] In the case of a ROM type optical disk, the optical recordinglayer 14 is composed of a reflection film made by aluminum, etc.

[0067] On the optical recording layer 14, a polymer film 16 produced,for example, by a melt cast method is stacked and adhered via anadhesive layer 15, so that the adhesive layer 15 and the polymer film 16compose a light transmitting protective film 17 having a film thicknessof 100 μm or so by putting the two together.

[0068] The above optical disk is a type wherein a laser light isirradiated on the optical recording layer 14 through the protective film17 and the reflected light is read. Due to this type, it is possible todeal with an objective lens of an increased numerical aperture in anoptical disk system.

[0069] For example, a large capacity of 22 GB or more can be attained inthe optical disk system by making the laser light wavelength 450 nm orless and the NA 0.78 or more and by using an optical disk wherein a thinlight transmitting protective film (a cover layer) of, for example, 100μm or so is formed.

[0070] The optical disk of the present embodiment is characterized inthat the thermal shrinkage coefficient of the polymer film 16 is 0.02%or less as in the polymer film produced, for example, by a melt castmethod, etc.

[0071] Here, the thermal shrinkage coefficient is a ratio of thermalshrinkage before and after annealing processing under a predeterminedcondition, such as annealing processing at 90° C. in the air for twohours, etc.

[0072] As the above polymer film 16, those subjected to annealingprocessing in advance to make the thermal shrinkage coefficient 0.02% orless after being produced to be a film and before being adhered to anoptical recording layer are preferably used.

[0073] Furthermore, a residual solvent in the polymer film is preferably0.3% by weight or less, and thereby, the thermal shrinkage coefficientcan be suppressed.

[0074] In an optical disk of the present embodiment, the lighttransmitting protective film includes a polymer film having a thermalshrinkage coefficient of 0.02% or less and an adhesive layer foradhering the polymer film to the optical recording layer, so thatshrinkage of the polymer film over a long time use can be suppressed andarising of warps on the optical recording medium can be suppressed.

[0075] The above polymer film 16 is preferably optically transparent andhas a low birefringent and a uniform film thickness. As a materialfulfilling these conditions, for example, resins of polycarbonate,cyclic polyolefin and polymethylmethacrylate (PMMA), etc. and a modifiedacrylic resin, etc. can be used.

[0076] The adhesive layer 15 for adhering the polymer film 16 to theoptical recording layer 14 to be used can be selected, for example, froman ultraviolet curing resin adhesive, a thermal curing resin adhesive,an epoxy resin adhesive and a pressures sensitive tackiness agent, etc.Alternately, two or more kinds of these may be mixed or stacked for use.

[0077] The adhesive strength by the adhesive layer 15 is made to be adegree of resisting a temperature change, a humidity change, an externalimpact, etc. and not causing any peeling.

[0078] The adhesive force depends on a material and film thickness ofthe optical recording layer 14 and those of the disk substrate 13 andthe polymer film 16, etc.

[0079] To prevent corrosion and other reaction to changerecording/reproducing properties of the optical recording layer 14 anddiffusion, it is necessary to adjust polymer, polymer resolvent,unreacting monomer, reaction initiator, equilibrium absorptionpercentage, etc. in the adhesive layer 15.

[0080] Next, a method of producing an optical disk of the presentembodiment will be explained with reference to cross-sectional views,schematic views or perspective views of respective production processes.

[0081] First, a resist disk RD wherein a resist film 11 is formed on aglass substrate 10 as shown in FIG. 3A is prepared.

[0082] As the above glass substrate 10, one having a diameter of, forexample, 200 mm or so and a finely polished surfaces is used.

[0083] Also, as the resist film 11, a resist of a type exposed, forexample, by an ultraviolet ray or an electron beam, etc. may be used,which has a film thickness of tens to 100 nm and is formed by a spincoat method, etc.

[0084] Next, as shown in a cross-sectional view in FIG. 3B, by using anultraviolet ray exposure apparatus or an electron beam exposureapparatus, etc., an electron beam exposure is performed on the resistfilm 11 by a pattern of exposing a region to be a groove or a pit of thedisk substrate and performing developing processing by using anexclusive liquid developer so as to obtain a resist film 11 a having apattern wherein a region to be a groove or a pit of the disk substrateis opened.

[0085] Next, as shown in a cross-sectional view in FIG. 4A, a stamper 12is formed on the above glass substrate 10 and the resist film 11 a, forexample, by performing nickel plating processing, etc.

[0086] On the surface of the stamper 12 is transferred an irregularitypattern which is an inverse of a groove 11 b formed by the resist film11 a and a projecting portion 12 a is formed.

[0087] Then, as shown in across-sectional view in FIG. 4B, the stamper12 is released from the glass substrate 10 and the resist film 11 a.

[0088] Then, as shown in a schematic view in FIG. 5A, the stamper 12obtained as above is fixed inside a cavity made by molds (MD1 and MD2)to compose an injection molding mold.

[0089] At this time, a projecting portion forming surface 12 a′ of thestamper 12 is arranged so as to face the inner surface of the cavity.

[0090] By injecting a polycarbonate resin, etc., for example, in a meltstate from an inlet IM of the mold inside the cavity of the aboveinjection molding mold, a disk substrate 13 is formed on theirregularity pattern of the stamper 12.

[0091] Here, the disk substrate 13 is transferred with a groove 13 a tobe a “groove” pattern or a “pit” pattern which is an inversedirregularity pattern of the irregularity pattern of the stamper 12.

[0092] By releasing from the above injection molding mold, the disksubstrate 13 being formed on its surface the groove 13 a to be a“groove” pattern or a “pit” pattern as shown in a cross-sectional viewin FIG. 6A is obtained.

[0093] Next, as shown in a cross-sectional view in FIG. 6B, afterremoving dust by blowing air or gas, such as a nitride gas, to thesurface of the disk substrate 13, an optical recording layer 14 having astacked body including a reflection film, a dielectric film, a recordingfilm and another dielectric film is formed by forming films in thisorder, for example, by a spattering method, etc.

[0094] As the above recording film, a recording film of a phase-changetype, a magneto-optical recording film or a recording film including anorganic dye may be used.

[0095] Alternately, in the case of a ROM type optical disk, the opticalrecording layer is formed by a reflection film of an aluminum layer,etc.

[0096] Next, a method of producing a polymer film by a melt cast methodwill be explained by referring to a schematic view in FIG. 7.

[0097] A polymer solution 22 obtained by resolving a polymer materialinto a solvent in a dissolution tank 21 and heating at a hightemperature is poured to an application tank 23, and the polymersolution 22 is applied to a smooth substrate or a belt 24 from anapplication outlet on the bottom of the application tank 23, so that apolymer solution applied film 25 is obtained.

[0098] The above polymer solution applied film 25 is dried, that is, thesolvent is evaporated while being left still or transferred on aconveyer belt 26 so as to obtain a film, which is wound together with aprotection film 27 and a polymer film roll 28 is obtained.

[0099] According to the melt cast method, when producing a polymer filmhaving a film thickness of, for example, 100 μm, a polymer solutiondiluted by five times by a solvent is prepared and applied to be a filmthickness of 500 μm. First, the film thickness is uniformized due toleveling at the time of application. An unevenness of the film thicknessat this time is, for example, ±5 μm or so, but when the applied filmdries to have a film thickness of 100 μm, the unevenness of the filmthickness is lessened to, for example, ±1 μm or so with respect to anaverage value. Thus, a film wherein a film thickness unevenness is smallcan be obtained.

[0100] When a film made by a polycarbonate resin is used as the abovepolymer film, dichloromethane (CH₂Cl₂) used as a solvent in the meltcast method remains in the film in some cases. The residual solventevaporates also after being adhered to the optical recording layer ofthe substrate composing an optical disk, so that a volume shrinkage ofthe polymer film is caused thereby and warps of the optical disk arise.

[0101] Accordingly, the less the residual solvent in the polymer filmmade by a polycarbonate resin, the better, and for example 0.3% byweight or less is preferable.

[0102] Here, those having a thermal shrinkage coefficient of 0.02% orless are used as the above polymer film.

[0103] Here, the thermal shrinkage coefficient is a ratio of thermalshrinkage before and after annealing processing under a predeterminedcondition, such as annealing processing at 90° C. in the air for twohours, etc.

[0104] When the thermal shrinkage coefficient of the polymer film ismore than 0.02%, it may be used by being subjected to annealingprocessing at 90° C. in the air for two hours, for example, by using acirculating drying furnace, a hot plate or an infrared heating furnaceto evaporate the residual solvent in the polymer film or to relaxinternal strain to make the thermal shrinkage coefficient within a rangeof 0.02% or less.

[0105] The annealing condition may be adjusted in accordance with athermal shrinkage coefficient of the polymer film.

[0106] The polymer film 16 s in a sheet shape produced as above may beused, for example, by being stamped out to be an optical disk size by astamping machine M as shown in a perspective view in FIG. 8.

[0107] In processes thereafter, the above polymer film is adhered via anadhesive layer to the optical recording layer 14 formed on the disksubstrate 13 shown in FIG. 6B.

[0108] First, as shown in a perspective view in FIG. 9A, an adhesive R,such as a liquid ultraviolet curing resin, a thermal curing resin or anepoxy resin, is supplied on the optical recording layer 14 by adispenser D while rotating the disk substrate 13.

[0109] Next, as shown in a perspective view in FIG. 9B, the polymer film16 composed of a polycarbonate resin, etc. produced by a melt castmethod and stamped out to be a disk shape is superimposed on the opticalrecording layer 14 on which the adhesive R is supplied. The polymer film16 is subjected to annealing processing in advance, if necessary.

[0110] Then, as shown in a perspective view in FIG. 10A, the adhesive Ris supplied evenly between the optical recording layer 14 and thepolymer film 16 due to a centrifugal force by spinning the disksubstrate 13 at a high speed, and an excessive adhesive is swished off.

[0111] Next, as shown in a perspective view in FIG. 10B, curingprocessing is performed, such as ultraviolet irradiation processing byan ultraviolet lamp UVL when the adhesive R is an ultraviolet curingresin, or thermal processing in the case of a thermal curing resin, sothat a cured adhesive layer 15 is obtained.

[0112] From the above processes, an optical disk having theconfiguration shown in FIG. 2 can be produced.

[0113] According to the method of producing an optical disk of thepresent embodiment as above, it is possible to produce an opticalrecording medium wherein a polymer film having a thermal shrinkagecoefficient of 0.02% or less is adhered to an optical recording layervia an adhesive layer as a light transmitting protective film, a polymerfilm shrinkage is suppressed during a long time use, and arising ofwarps is suppressed.

[0114] Second Embodiment

[0115] The configuration of an optical disk according to the presentembodiment is the same as that of an optical disk according to the firstembodiment. Note that it is different in using an adhesive film, such asa pressure sensitive tackiness agent film, as an adhesive layer 15 foradhering a polymer film 16 to an optical recording layer 14.

[0116] For example, when assuming that a film thickness of a protectivefilm is 100 μm, a film thickness of the adhesive layer made of atackiness agent is made to be 25 μm and that of the polymer film 75 μm.

[0117] A method of producing the above optical disk of the presentembodiment will be explained with reference to drawings.

[0118] First, as shown in a perspective view in FIG. 11A, a stackedtackiness agent film ST wherein a tackiness agent film TA is sandwichedby two PET (polyethylene terephthalate) liners (PL1 and PL2) isprepared.

[0119] Next, as shown in a perspective view in FIG. 11B, the abovestacked tackiness agent film ST is stamped out to be an optical disksize by a stamping machine M.

[0120] Then, as shown in a perspective view in FIG. 12A, the PET linerPL1 on one side of the above stacked tackiness agent film ST stamped outto be an optical disk size is peeled.

[0121] Next, as shown in a perspective view in FIG. 12B, a thus obtainedtackiness agent film TA having the PET liner PL2 on its one side is seton a base S having a projection for aligning at the center, and thereon,a disk substrate 13 made by a polycarbonate resin, etc. on which anoptical recording layer 14 formed by the separated process in the sameway as in the first embodiment is aligned to be set with its opticalrecording layer 14 side facing to the tackiness agent film TA side.

[0122] Then, as shown in a perspective view in FIG. 13A, a pressure isgiven on the disk substrate 13 from above by a pad P or a roller, etc.,so that the optical recording layer 14 formed on the disk substrate 13and the tackiness agent film TA are sufficiently adhered.

[0123] Next, as shown in a perspective view in FIG. 13B, the PET linerPL2 remained on the other side of the tackiness agent film TA is peeledoff.

[0124] Next, as shown in a perspective view in FIG. 14A, a polymer film16 formed by the separated process in advance is set on the base Shaving a projection for aligning at the center, and thereon, the disksubstrate 13 being adhered the above tackiness agent film TA is alignedto be set with the tackiness agent film TA side facing to the polymerfilm 16 side.

[0125] Then, as shown in a perspective view in FIG. 14B, a pressure isgiven on the disk substrate 13 from above by a pad P or a roller, etc.,so that the polymer film 16 and the tackiness agent film TA aresufficiently adhered.

[0126] From the above processes, an optical disk wherein the adhesivelayer 15 is composed of the tackiness agent film TA in the configurationshown in FIG. 2 can be produced.

[0127] According to the method of producing an optical disk of the abovepresent embodiment, it is possible to produce an optical recordingmedium wherein a polymer film having a thermal shrinkage coefficient of0.02% or less is adhered to an optical recording layer via an adhesivelayer as a light transmitting protective film, shrinkage of a polymerfilm is suppressed during a long time use, and arising of warps issuppressed.

EXAMPLE 1

[0128] Polymer films made by a polycarbonate resin was prepared by amelt cast method.

[0129] Namely, dichloromethane was used as a solvent, a solution of apolycarbonate resin and dichloromethane was applied thinly on a cast ata high temperature and dried to prepare polymer films having a filmthickness of 75 μm.

[0130] At this time, polymer films having a different thermal shrinkagecoefficient were obtained by adjusting a drying condition and a tensionat the time of pulling up the film.

[0131] Next, an irregularity pattern for optical recording layer isformed on the polycarbonate substrate having an outer diameter of 120mm, an inner diameter of 15 mm and a thickness of 1.1 mm by injectionmolding, an aluminum optical recording layer is formed thereon, apressure sensitive tackiness agent film (CS9603 made by Nitto DenkoCorporation) having a film thickness of 25 μm is adhered on its surface,and the above polycarbonate film is adhered thereon to prepare samples.

[0132] Here, seven kinds of films wherein the thermal shrinkagecoefficient was different (0.01%, 0.02%, 0.03%, 0.05%, 0.09%, 0.12% and0.15%) were used as the polycarbonate film to prepare four optical disksamples.

[0133] As an accelerate condition, the above optical disk samples wereleft for 96 hours under a high temperature and high humidity atmosphereof a temperature of 80° C. and a humidity of 85%, and changes of aradial skew were measured before and after that.

[0134] Here, in a state where the center portion of the disk was held ona reference plane, a light vertical with respect to a reference planewas irradiated to the surface of a disk edge portion and a reflectionangle of an obtained reflected light was measured so as to measure aninclination of the surface at the disk edge portion as the radial skew.

[0135] Since a value of the radial skew becomes maximum at the outerdiameter of the disk, measurement was made at a position at a radius of58 mm in the present example.

[0136] The results are shown in Table 1. TABLE 1 Thermal ShrinkageCoefficient Radial Skew Change (%) (degree) 0.01 −0.04 0.02 −0.09 0.03−0.13 0.05 −0.24 0.09 −0.71 0.12 −1.01 0.15 −1.20

[0137] From the Table 1, a change value of the radial skew becomessmaller as the thermal shrinkage coefficient becomes smaller, while thechange value of the radial skew becomes larger as the thermal shrinkagecoefficient becomes larger.

[0138] It was found that a change of the radial skew was preferablywithin ±0.1 degree and to attain the range the thermal shrinkagecoefficient of the polymer film has to be 0.02% or less.

EXAMPLE 2

[0139] Next, polymer films having a thermal shrinkage coefficient ofover 0.02% (0.03%, 0.05% and 0.09%) were subjected to annealingprocessing at 90° C. in the air for two hours by a hot plate in advanceprior to adhesion so that the same samples as the above were preparedand a change value of a radial skew was measured in the same way as theabove.

[0140] The results are shown in Table 2. TABLE 2 Thermal ShrinkageCoefficient Thermal Shrinkage Before Annealing Coefficient After RadialSkew (%) Annealing (%) Change (degree) 0.03 0.01 −0.06 0.05 0.01 −0.080.09 0.02 −0.09

[0141] From Table 2, it was found that the polymer films having athermal shrinkage coefficient of over 0.02% could be made to have athermal shrinkage coefficient in a range of 0.02% or less by beingsubjected to the annealing processing and a change of a radial skew whenusing this polymer film was suppressed to be within ±0.1 degree.

[0142] Note that in the above experiments, a difference from a changeamount of a radial skew was measured by using a disk substrate wherein apolymer film is not adhered as a reference so as to eliminate a changeamount of the disk substrate due to thermal processing.

[0143] The present invention is not limited to the above embodiments.

[0144] For example, a material and film thickness, etc. of a substratecomposing an optical recording medium, optical recording layer and anadhesive layer between layers, etc. are not limited to those explainedin the above embodiments and may be suitably selected.

[0145] Also, as a polymer film, those produced by a method other thanthe melt cast method can be used as far as the thermal shrinkagecoefficient is 0.02% or less, and a material and a film thickness, etc.can be suitably selected.

[0146] Other than the above, a variety of modifications can be madewithin a scope of the present invention.

[0147] According to an optical recording medium of the presentinvention, a thermal shrinkage coefficient of a polymer film composing alight transmitting protective film is 0.02% or less, and thereby,shrinkage of the polymer film can be suppressed over a long time use andarising of warps on the optical recording medium can be suppressed.

[0148] Also, according to a method of producing an optical recordingmedium of the present invention, it is possible to produce an opticalrecording medium wherein a polymer film having a thermal shrinkagecoefficient of 0.02% or less is adhered to an optical recording layer asa light transmitting protective film, so that shrinkage of the polymerfilm is suppressed over a long time use and arising of warps aresuppressed.

INDUSTRIAL APPLICABILITY

[0149] An optical recording medium of the present invention can beapplied to an optical recording medium for optically recording a largeamount of information on an optical recording layer.

[0150] A method of producing an optical recording medium of the presentinvention can be applied to a method of producing an optical recordingmedium according to the above present invention.

1. An optical recording medium, comprising: a substrate; an opticalrecording medium formed on said substrate; and a light transmittingprotective film formed on said optical recording layer; wherein saidprotective film comprises a polymer film having a thermal shrinkagecoefficient of 0.02% or less and an adhesive layer for adhering saidpolymer film to said optical recording layer.
 2. An optical recordingmedium as set forth in claim 1, wherein said polymer film is a polymerfilm produced by a melt cast method.
 3. An optical recording medium asset forth in claim 1, wherein said polymer film is a polymer filmsubjected to annealing processing after being produced as a film andbefore being adhered to said optical recording layer in advance.
 4. Anoptical recording medium as set forth in claim 1, wherein a residualsolvent in said polymer film is 0.3% by weight or less.
 5. A method ofproducing an optical recording medium, including the steps of: formingan optical recording layer on a substrate; and forming a lighttransmitting protective film on said optical recording layer; whereinthe step of forming said protective film includes a step of adhering apolymer film having a thermal shrinkage coefficient of 0.02% or less tosaid optical recording layer via an adhesive layer.
 6. A method ofproducing an optical recording medium as set forth in claim 5, wherein apolymer film produced by a melt cast method is used as said polymerfilm.
 7. A method of producing an optical recording medium as set forthin claim 5, wherein annealing processing is performed on said polymerfilm after the step of producing the polymer film as a film and beforethe step of adhering to said optical recording layer in advance.
 8. Amethod of producing an optical recording medium as set forth in claim 5,wherein a polymer film wherein a residual solvent in the polymer film is0.3% by weight or less is used as said polymer film.